ABSTRACT
Academic health centers (AHCs) are the nation's primary resource for healthcare discovery, innovation, and training. US healthcare revenue growth has declined sharply since 2009, and is forecast to remain well below historic levels for the foreseeable future. As the cost of education and research at nearly all AHCs is heavily subsidized through large transfers from clinical care margins, our institutions face a mounting crisis. Choices centering on how to increase the cost-effectiveness of the AHC enterprise require unprecedented levels of alignment to preserve an environment that nurtures creativity. Management processes require governance models that clarify decision rights while harnessing the talents and the intellectual capital of a large, diverse enterprise to nimbly address unfamiliar organizational challenges. This paper describes key leadership tactics aimed at propelling AHCs along this journey - one that requires from all leaders a commitment to resilience, optimism, and willingness to embrace change.
Subject(s)
Academic Medical Centers/organization & administration , Delivery of Health Care , Hospital Administration , Humans , Leadership , Models, Organizational , Organizational Affiliation , United StatesABSTRACT
The human Ether-à-go-go-related gene (hERG)-encoded K(+) current, I(Kr) is essential for cardiac repolarization but is also a source of cardiotoxicity because unintended hERG inhibition by diverse pharmaceuticals can cause arrhythmias and sudden cardiac death. We hypothesized that a small molecule that diminishes I(Kr) block by a known hERG antagonist would constitute a first step toward preventing hERG-related arrhythmias and facilitating drug discovery. Using a high-throughput assay, we screened a library of compounds for agents that increase the IC(70) of dofetilide, a well characterized hERG blocker. One compound, VU0405601, with the desired activity was further characterized. In isolated, Langendorff-perfused rabbit hearts, optical mapping revealed that dofetilide-induced arrhythmias were reduced after pretreatment with VU0405601. Patch clamp analysis in stable hERG-HEK cells showed effects on current amplitude, inactivation, and deactivation. VU0405601 increased the IC(50) of dofetilide from 38.7 to 76.3 nM. VU0405601 mitigates the effects of hERG blockers from the extracellular aspect primarily by reducing inactivation, whereas most clinically relevant hERG inhibitors act at an inner pore site. Structure-activity relationships surrounding VU0405601 identified a 3-pyridiyl and a naphthyridine ring system as key structural components important for preventing hERG inhibition by multiple inhibitors. These findings indicate that small molecules can be designed to reduce the sensitivity of hERG to inhibitors.
Subject(s)
Arrhythmias, Cardiac/chemically induced , Arrhythmias, Cardiac/drug therapy , Ether-A-Go-Go Potassium Channels/antagonists & inhibitors , Ether-A-Go-Go Potassium Channels/metabolism , Muscle Proteins/antagonists & inhibitors , Muscle Proteins/metabolism , Naphthyridines/chemistry , Naphthyridines/pharmacology , Phenethylamines/adverse effects , Potassium Channel Blockers/adverse effects , Pyridines/chemistry , Pyridines/pharmacology , Sulfonamides/adverse effects , Animals , Arrhythmias, Cardiac/metabolism , Arrhythmias, Cardiac/pathology , Dose-Response Relationship, Drug , Drug Discovery , ERG1 Potassium Channel , Ether-A-Go-Go Potassium Channels/genetics , HEK293 Cells , Humans , Muscle Proteins/genetics , Myocardium/metabolism , Myocardium/pathology , Phenethylamines/pharmacology , Potassium Channel Blockers/pharmacology , Rabbits , Structure-Activity Relationship , Sulfonamides/pharmacologyABSTRACT
Large-scale DNA databanks linked to electronic medical record (EMR) systems have been proposed as an approach for rapidly generating large, diverse cohorts for discovery and replication of genotype-phenotype associations. However, the extent to which such resources are capable of delivering on this promise is unknown. We studied whether an EMR-linked DNA biorepository can be used to detect known genotype-phenotype associations for five diseases. Twenty-one SNPs previously implicated as common variants predisposing to atrial fibrillation, Crohn disease, multiple sclerosis, rheumatoid arthritis, or type 2 diabetes were successfully genotyped in 9483 samples accrued over 4 mo into BioVU, the Vanderbilt University Medical Center DNA biobank. Previously reported odds ratios (OR(PR)) ranged from 1.14 to 2.36. For each phenotype, natural language processing techniques and billing-code queries were used to identify cases (n = 70-698) and controls (n = 808-3818) from deidentified health records. Each of the 21 tests of association yielded point estimates in the expected direction. Previous genotype-phenotype associations were replicated (p < 0.05) in 8/14 cases when the OR(PR) was > 1.25, and in 0/7 with lower OR(PR). Statistically significant associations were detected in all analyses that were adequately powered. In each of the five diseases studied, at least one previously reported association was replicated. These data demonstrate that phenotypes representing clinical diagnoses can be extracted from EMR systems, and they support the use of DNA resources coupled to EMR systems as tools for rapid generation of large data sets required for replication of associations found in research cohorts and for discovery in genome science.
Subject(s)
Arthritis, Rheumatoid/genetics , Atrial Fibrillation/genetics , Crohn Disease/genetics , Diabetes Mellitus, Type 2/genetics , Electronic Health Records , Genetic Association Studies/trends , Multiple Sclerosis/genetics , Case-Control Studies , DNA/blood , DNA/genetics , Genome, Human , Genome-Wide Association Study , Genotype , Humans , Phenotype , Polymorphism, Single Nucleotide/geneticsABSTRACT
The human ether-a-go-go related gene (HERG) constitutes the pore forming subunit of I(Kr), a K(+) current involved in repolarization of the cardiac action potential. While mutations in HERG predispose patients to cardiac arrhythmias (Long QT syndrome; LQTS), altered function of HERG regulators are undoubtedly LQTS risk factors. We have combined RNA interference with behavioral screening in Caenorhabditis elegans to detect genes that influence function of the HERG homolog, UNC-103. One such gene encodes the worm ortholog of the rho-GTPase activating protein 6 (ARHGAP6). In addition to its GAP function, ARHGAP6 induces cytoskeletal rearrangements and activates phospholipase C (PLC). Here we show that I(Kr) recorded in cells co-expressing HERG and ARHGAP6 was decreased by 43% compared to HERG alone. Biochemical measurements of cell-surface associated HERG revealed that ARHGAP6 reduced membrane expression of HERG by 35%, which correlates well with the reduction in current. In an atrial myocyte cell line, suppression of endogenous ARHGAP6 by virally transduced shRNA led to a 53% enhancement of I(Kr). ARHGAP6 effects were maintained when we introduced a dominant negative rho-GTPase, or ARHGAP6 devoid of rhoGAP function, indicating ARHGAP6 regulation of HERG is independent of rho activation. However, ARHGAP6 lost effectiveness when PLC was inhibited. We further determined that ARHGAP6 effects are mediated by a consensus SH3 binding domain within the C-terminus of HERG, although stable ARHGAP6-HERG complexes were not observed. These data link a rhoGAP-activated PLC pathway to HERG membrane expression and implicate this family of proteins as candidate genes in disorders involving HERG.
Subject(s)
Caenorhabditis elegans/genetics , Caenorhabditis elegans/metabolism , Ether-A-Go-Go Potassium Channels/metabolism , GTPase-Activating Proteins/metabolism , Animals , Arrhythmias, Cardiac/genetics , Arrhythmias, Cardiac/metabolism , Caenorhabditis elegans Proteins/genetics , Caenorhabditis elegans Proteins/metabolism , ERG1 Potassium Channel , Electrophysiology , Ether-A-Go-Go Potassium Channels/genetics , GTPase-Activating Proteins/genetics , Humans , Long QT Syndrome/genetics , Long QT Syndrome/metabolism , Potassium/metabolism , Potassium Channels/genetics , Potassium Channels/metabolism , RNA InterferenceABSTRACT
The pore of the Na+ channel is lined by asymmetric loops formed by the linkers between the fifth and sixth transmembrane segments (S5-S6). We investigated the role of the N-terminal portion (SS1) of the S5-S6 linkers in channel gating and local anesthetic (LA) block using site-directed cysteine mutagenesis of the rat skeletal muscle (Na(V)1.4) channel. The mutants examined have variable effects on voltage dependence and kinetics of fast inactivation. Of the cysteine mutants immediately N-terminal to the putative DEKA selectivity filter in four domains, only Q399C in domain I and F1236C in domain III exhibit reduced use-dependent block. These two mutations also markedly accelerated the recovery from use-dependent block. Moreover, F1236C and Q399C significantly decreased the affinity of QX-314 for binding to its channel receptor by 8.5- and 3.3-fold, respectively. Oddly enough, F1236C enhanced stabilization of slow inactivation by both hastening entry into and delaying recovery from slow inactivation states. It is noteworthy that symmetric applications of QX-314 on both external and internal sides of F1236C mutant channels reduced recovery from use-dependent block, indicating an allosteric effect of external QX-314 binding on the recovery of availability of F1236C. These observations suggest that cysteine mutation in the SS1 region, particularly immediate adjacent to the DEKA ring, may lead to a structural rearrangement that alters binding of permanently charged QX-314 to its receptor. The results lend further support for a role for the selectivity filter region as a structural determinant for local anesthetic block.
Subject(s)
Anesthetics, Local/pharmacology , Muscle Proteins/metabolism , Muscle, Skeletal/drug effects , Sodium Channels/metabolism , Anesthetics, Local/metabolism , Animals , Ion Channel Gating , Kinetics , Muscle Proteins/chemistry , Muscle Proteins/genetics , Muscle, Skeletal/metabolism , Mutagenesis, Site-Directed , Rats , Sodium Channels/chemistry , Sodium Channels/geneticsABSTRACT
Human ether-a-go-go-related gene (HERG) encodes the rapid, outwardly rectifying K(+) current I(Kr) that is critical for repolarization of the cardiac action potential. Congenital HERG mutations or unintended pharmaceutical block of I(Kr) can lead to life-threatening arrhythmias. Here, we assess the functional role of the alanine at position 653 (HERG-A653) that is highly conserved among evolutionarily divergent K(+) channels. HERG-A653 is close to the 'glycine hinge' implicated in K(+) channel opening, and is flanked by tyrosine 652 and phenylalanine 656, which contribute to the drug binding site. We substituted an array of seven (I, C, S, G, Y, V and T) amino acids at position 653 and expressed individual variants in heterologous systems to assess changes in gating and drug binding. Substitution of A653 resulted in negative shifts of the V(1/2) of activation ranging from -23.6 (A653S) to -62.5 (A653V) compared to -11.2 mV for wild-type (WT). Deactivation was also drastically altered: channels with A653I/C substitutions exhibited delayed deactivation in response to test potentials above the activation threshold, while A653S/G/Y/V/T failed to deactivate under those conditions and required hyperpolarization and prolonged holding potentials at -130 mV. While A653S/G/T/Y variants showed decreased sensitivity to the I(Kr) inhibitor dofetilide, these changes could not be correlated with defects in channel closure. Homology modelling suggests that in the closed state, A653 forms tight contacts with several residues from the neighbouring subunit in the tetramer, playing a key role in S6 helix packing at the narrowest part of the vestibule. Our study suggests that A653 plays an important functional role in the outwardly rectifying gating behaviour of HERG, supporting channel closure at membrane potentials negative to the channel activation threshold.
Subject(s)
Conserved Sequence , Ether-A-Go-Go Potassium Channels/metabolism , Evolution, Molecular , Ion Channel Gating , Alanine , Amino Acid Sequence , Animals , CHO Cells , Computer Simulation , Cricetinae , Cricetulus , ERG1 Potassium Channel , Ether-A-Go-Go Potassium Channels/antagonists & inhibitors , Ether-A-Go-Go Potassium Channels/chemistry , Ether-A-Go-Go Potassium Channels/genetics , Humans , Kinetics , Membrane Potentials , Models, Molecular , Molecular Sequence Data , Mutation , Oocytes , Phenethylamines/pharmacology , Potassium Channel Blockers/pharmacology , Protein Conformation , Structure-Activity Relationship , Sulfonamides/pharmacology , Transfection , Xenopus laevisABSTRACT
Sodium channels initiate the electrical cascade responsible for cardiac rhythm, and certain life-threatening arrhythmias arise from Na(+) channel dysfunction. We propose a novel mechanism for modulation of Na(+) channel function whereby calcium ions bind directly to the human cardiac Na(+) channel (hH1) via an EF-hand motif in the C-terminal domain. A functional role for Ca(2+) binding was identified electrophysiologically, by measuring Ca(2+)-induced modulation of hH1. A small hH1 fragment containing the EF-hand motif was shown to form a structured domain and to bind Ca(2+) with affinity characteristic of calcium sensor proteins. Mutations in this domain reduce Ca(2+) affinity in vitro and the inactivation gating effects of Ca(2+) in electrophysiology experiments. These studies reveal the molecular basis for certain forms of long QT syndrome and other arrhythmia-producing syndromes, and suggest a potential pharmacological target for antiarrhythmic drug design.
Subject(s)
Calcium/pharmacology , EF Hand Motifs/physiology , Heart/physiology , Sodium Channels/physiology , Amino Acid Sequence , Binding Sites , Calmodulin , EF Hand Motifs/genetics , Electrophysiology , Humans , Models, Biological , Mutation , Sodium Channels/chemistry , Sodium Channels/drug effects , Spectrum AnalysisABSTRACT
Our understanding of the genetic basis of disease has expanded with the identification of rare DNA sequence variations ("mutations") that evoke inherited syndromes such as cystic fibrosis, congenital epilepsy, and cardiac arrhythmias. Common sequence variants ("polymorphisms") have also been implicated as risk factors in multiple diseases. Mutations in SCN5A, the cardiac Na(+) channel gene, that cause a reduction in Na(+) current may evoke severe, life-threatening disturbances in cardiac rhythm (i.e., Brugada syndrome), isolated cardiac conduction disease, or combinations of these disorders. Conduction disease is manifest clinically as heart rate slowing (bradycardia), syncope, or "lightheadedness". Recent electrophysiologic studies reveal that mutations in particular families exhibiting cardiac conduction disease cause marked effects on several competing voltage-dependent gating processes, but nonetheless cause a mild "net" reduction in Na(+) current. Here we show that a common SCN5A polymorphism (H558R) in the Na(+) channel I-II interdomain cytoplasmic linker, present in 20% of the population, can mitigate the in vitro effects of a nearby mutation (T512I) on Na(+) channel function. The mutation and the polymorphism were both found in the same allele of a child with isolated conduction disease, suggesting a direct functional association between a polymorphism and a mutation in the same gene.
Subject(s)
Mutation , Polymorphism, Genetic , Sodium Channels/genetics , Alleles , Base Sequence , DNA, Complementary/metabolism , Electrophysiology , Family Health , Female , Genotype , Humans , Infant , Male , Membrane Potentials , Molecular Sequence Data , NAV1.5 Voltage-Gated Sodium Channel , Pedigree , PhenotypeABSTRACT
Sudden cardiac death attributable to ventricular tachycardia/fibrillation (VF) remains a catastrophic outcome of myocardial ischemia and infarction. At the same time, conventional antagonist drugs targeting ion channels have yielded poor survival benefits. Although pharmacological and genetic models suggest an association between sodium (Na+) channel loss-of-function and sudden cardiac death, molecular mechanisms have not been identified that convincingly link ischemia to Na+ channel dysfunction and ventricular arrhythmias. Because ischemia can evoke the generation of reactive oxygen species, we explored the effect of oxidative stress on Na+ channel function. We show here that oxidative stress reduces Na+ channel availability. Both the general oxidant tert-butyl-hydroperoxide and a specific, highly reactive product of the isoprostane pathway of lipid peroxidation, E2-isoketal, potentiate inactivation of cardiac Na+ channels in human embryonic kidney (HEK)-293 cells and cultured atrial (HL-1) myocytes. Furthermore, E2-isoketals were generated in the epicardial border zone of the canine healing infarct, an arrhythmogenic focus where Na+ channels exhibit similar inactivation defects. In addition, we show synergistic functional effects of flecainide, a proarrhythmic Na+ channel blocker, and oxidative stress. These data suggest Na+ channel dysfunction evoked by lipid peroxidation is a candidate mechanism for ischemia-related conduction abnormalities and arrhythmias.
Subject(s)
Arrhythmias, Cardiac/etiology , Lipid Peroxidation , Myocardium/metabolism , Sodium Channels/physiology , Aldehydes/pharmacology , Cell Line , Flecainide/pharmacology , Humans , Isoprostanes/metabolism , Myocardial Infarction/metabolism , Oxidative Stress , tert-Butylhydroperoxide/pharmacologyABSTRACT
BACKGROUND: Three distinct cardiac arrhythmia disorders, the long-QT syndrome, Brugada syndrome, and conduction system disease, have been associated with heterozygous mutations in the cardiac voltage-gated sodium channel alpha-subunit gene (SCN5A). We present clinical, genetic, and biophysical features of 2 new SCN5A mutations that result in atrioventricular (AV) conduction block. Methods and Results- SCN5A was used as a candidate gene in 2 children with AV block. Molecular genetic studies revealed G to A transition mutations that resulted in the substitution of serine for glycine (G298S) in the domain I S5-S6 loop and asparagine for aspartic acid (D1595N) within the S3 segment of domain IV. The functional consequences of G298S and D1595N were assessed by whole-cell patch clamp recording of recombinant mutant channels coexpressed with the beta1 subunit in a cultured cell line (tsA201). Both mutations impair fast inactivation but do not exhibit sustained non-inactivating currents. The mutations also reduce sodium current density and enhance slower inactivation components. Action potential simulations predict that this combination of biophysical abnormalities will significantly slow myocardial conduction velocity. CONCLUSIONS: A distinct pattern of biophysical abnormalities not previously observed for any other SCN5A mutant have been recognized in association with AV block. These data provide insight into the distinct clinical phenotypes resulting from mutation of a single ion channel.
Subject(s)
Atrioventricular Node , Heart Block/genetics , Mutation , Sodium Channels/genetics , Action Potentials , Adult , Amino Acid Sequence , Atrioventricular Node/physiopathology , Cell Line , Child , Computer Simulation , Electrocardiography , Female , Heart Block/diagnosis , Heart Block/physiopathology , Humans , Kinetics , Male , Middle Aged , Molecular Sequence Data , NAV1.5 Voltage-Gated Sodium Channel , Patch-Clamp Techniques , Protein Structure, Tertiary , Sequence Homology, Amino Acid , Sodium Channels/chemistry , Sodium Channels/metabolismABSTRACT
Most voltage-gated K(+) currents are relatively insensitive to extracellular Na(+) (Na(+)(o)), but Na(+)(o) potently inhibits outward human ether-a-go-go-related gene (HERG)-encoded K(+) channel current (Numaguchi, H., J.P. Johnson, Jr., C.I. Petersen, and J.R. Balser. 2000. Nat. Neurosci. 3:429-30). We studied wild-type (WT) and mutant HERG currents and used two strategic probes, intracellular Na(+) (Na(+)(i)) and extracellular Ba(2+) (Ba(2+)(o)), to define a site where Na(+)(o) interacts with HERG. Currents were recorded from transfected Chinese hamster ovary (CHO-K1) cells using the whole-cell voltage clamp technique. Inhibition of WT HERG by Na(+)(o) was not strongly dependent on the voltage during activating pulses. Three point mutants in the P-loop region (S624A, S624T, S631A) with intact K(+) selectivity and impaired inactivation each had reduced sensitivity to inhibition by Na(+)(o). Quantitatively similar effects of Na(+)(i) to inhibit HERG current were seen in the WT and S624A channels. As S624A has impaired Na(+)(o) sensitivity, this result suggested that Na(+)(o) and Na(+)(i) act at different sites. Extracellular Ba(2+) (Ba(2+)(o)) blocks K(+) channel pores, and thereby serves as a useful probe of K(+) channel structure. HERG channel inactivation promotes relief of Ba(2+) block (Weerapura, M., S. Nattel, M. Courtemanche, D. Doern, N. Ethier, and T. Hebert. 2000. J. Physiol. 526:265-278). We used this feature of HERG inactivation to distinguish between simple allosteric and pore-occluding models of Na(+)(o) action. A remote allosteric model predicts that Na(+)(o) will speed relief of Ba(2+)(o) block by promoting inactivation. Instead, Na(+)(o) slowed Ba(2+) egress and Ba(2+) relieved Na(+)(o) inhibition, consistent with Na(+)(o) binding to an outer pore site. The apparent affinities of the outer pore for Na(+)(o) and K(+)(o) as measured by slowing of Ba(2+) egress were compatible with competition between the two ions for the channel pore in their physiological concentration ranges. We also examined the role of the HERG closed state in Na(+)(o) inhibition. Na(+)(o) inhibition was inversely related to pulsing frequency in the WT channel, but not in the pore mutant S624A.
Subject(s)
Cation Transport Proteins , Ion Channel Gating/physiology , Potassium Channels, Voltage-Gated/physiology , Potassium Channels/physiology , Sodium/pharmacology , Animals , Barium/pharmacokinetics , CHO Cells , Cricetinae , Electrophysiology , Ether-A-Go-Go Potassium Channels , Potassium Channels/genetics , Sodium/pharmacokineticsABSTRACT
The cardiac potassium channel encoded by the human ether-à-go-go related gene (HERG) is blocked by a diverse array of common therapeutic compounds. Even transient exposure to such agents may provoke the life-threatening cardiac arrhythmia torsades de pointes in some, but not all, individuals. Although the molecular and genetic factors predicting such wide variability in drug response remain unclear, known sequence variations within the coding region of HERG do not explain the adverse drug response in many cases. Although other proteins can modulate HERG function, no studies have identified protein partners capable of limiting the pharmacological sensitivity of HERG. Here we show that KCR1, a protein identified previously in rat cerebellum, is a plasma membrane-associated protein expressed at the RNA level in the human heart and can be immunoprecipitated with HERG. Functionally, KCR1 reduces the sensitivity of HERG to classic proarrhythmic HERG blockers (sotalol, quinidine, dofetilide) in both cardiac and noncardiac cell lines. We propose that KCR1, when coupled to HERG, may limit the sensitivity of HERG to proarrhythmic drug blockade and may be a rational target for modifying the proarrhythmic effects of otherwise clinically useful compounds.
Subject(s)
Anti-Arrhythmia Agents/pharmacology , Cation Transport Proteins , DNA-Binding Proteins , Myocytes, Cardiac/physiology , Nerve Tissue Proteins/physiology , Potassium Channel Blockers/pharmacology , Potassium Channels, Voltage-Gated , Potassium Channels/physiology , Trans-Activators , Animals , Anti-Arrhythmia Agents/antagonists & inhibitors , CHO Cells , Cell Line , Cricetinae , ERG1 Potassium Channel , Electric Conductivity , Ether-A-Go-Go Potassium Channels , Glucosyltransferases/metabolism , Humans , Ion Channel Gating , Membrane Transport Proteins/metabolism , Models, Biological , Myocardium/metabolism , Myocytes, Cardiac/drug effects , Nerve Tissue Proteins/genetics , Potassium Channel Blockers/antagonists & inhibitors , Potassium Channels/genetics , Transcriptional Regulator ERG , TransfectionABSTRACT
Voltage-gated sodium channels are transmembrane proteins that produce the ionic current responsible for the rising phase of the cardiac action potential and play a fundamental role in the initiation, propagation, and maintenance of normal cardiac rhythm. Inherited mutations in SCN5A, the gene encoding the pore-forming subunit of the cardiac Na+ channel, have been associated with distinct cardiac rhythm syndromes: the congenital long QT syndrome, Brugada syndrome, and isolated conduction disease. Electrophysiologic characterization of heterologously expressed mutant Na+ channels have revealed gating defects that, in many cases, can explain the distinct phenotype associated with the rhythm disorder. However, recent studies have revealed significant overlap between aberrant rhythm phenotypes, and single mutations have been identified that evoke multiple rhythm disorders with common gating lesions. These new insights enhance understanding of the structure-function relationships of voltage-gated Na+ channels, and also highlight the complexities involved in linking single mutations, ion-channel behavior, and cardiac rhythm.
Subject(s)
Arrhythmias, Cardiac/genetics , Sodium Channels/physiology , Arrhythmias, Cardiac/drug therapy , Arrhythmias, Cardiac/metabolism , Female , Genetic Predisposition to Disease , Heart Conduction System/physiology , Humans , Long QT Syndrome/drug therapy , Long QT Syndrome/genetics , Long QT Syndrome/metabolism , Male , Mutagenesis, Site-Directed , Prognosis , Risk Assessment , Sodium Channel Blockers/therapeutic use , Sodium Channels/geneticsABSTRACT
OBJECTIVE: Co-expression of the KvLQT1 and minK potassium channel subunits is required to recapitulate I(Ks), the slow component of the cardiac delayed rectifier current, and mutations in either gene cause the congenital Long QT syndrome. It is becoming increasingly well-recognized that multiprotein channel complexes containing proteins capable of modulating channel function assemble at the plasma membrane. Thus, the aim of our study was to identify proteins involved in I(Ks) modulation. METHODS AND RESULTS: Using a yeast-two-hybrid screen with the intracytoplasmic C-terminus of minK as bait, we identified the cardiac-enriched four-and-a-half LIM domain-containing protein (fhl2) as a potential minK partner. We show interaction between the two proteins in GST pulldown assays and demonstrate overlapping subcellular localization using immunocytochemistry of transfected cells supporting a potential interaction. At the functional level, expression of KvLQT1and minK in HEK cells, which lack endogenous fhl2 protein, generated I(Ks) only when fhl2 was co-expressed. By contrast, in CHO-K1 cells, which express fhl2 endogenously, I(Ks) was suppressed by anti-fhl2 antisense which did not affect the currents generated by KvLQT1alone. CONCLUSION: These data indicate that at least in heterologous cells, the generation of I(Ks) requires fhl2 as an additional protein component.
Subject(s)
Cell Membrane/metabolism , Homeodomain Proteins/metabolism , Potassium Channels, Voltage-Gated/metabolism , Transcription Factors , Animals , CHO Cells , Cricetinae , Genetic Engineering , Homeodomain Proteins/genetics , Homeodomain Proteins/isolation & purification , Immunohistochemistry , KCNQ Potassium Channels , KCNQ1 Potassium Channel , Long QT Syndrome/metabolism , Oligonucleotides, Antisense/pharmacology , Patch-Clamp Techniques , Potassium Channels/metabolism , Potassium Channels, Voltage-Gated/genetics , Transfection , Two-Hybrid System TechniquesABSTRACT
Reductions in federal support and clinical revenue jeopardize biomedical research and, in turn, clinical medicine.
Subject(s)
Academic Medical Centers , Biomedical Research , Humans , UncertaintyABSTRACT
One hundred years after Flexner wrote his report for the Carnegie Foundation, calls are heard for another "Flexnerian revolution," a reform movement that would overhaul an approach to medical education that is criticized for its expense and inefficiency, its failure to respond to the health needs of our communities, and the high cost and inefficiency of the health care system it supports. To address these concerns, a group of Vanderbilt educators, national experts, administrators, residents, and students attended a retreat in November 2008. The goal of this meeting was to craft a new vision of physician learning based on the continuous development and assessment of competencies needed for effective and compassionate care under challenging circumstances. The vision that emerged from this gathering was that of a health care workforce comprised of physicians and other professionals, all capable of assessing practice outcomes, identifying learning needs, and engaging in continuous learning to achieve the best care for their patients. Several principles form the foundation for this vision. Learning should be competency based and embedded in the workplace. It should be linked to patient needs and undertaken by individual providers, by teams, and by institutions. Health professionals should be trained in this new model from the start of the educational experience, leading to true interprofessional education, with shared facilities and the same basic coursework. Multiple entry and exit points would provide flexibility and would allow health professionals to redirect their careers as their goals evolved. This article provides a detailed account of the model developed at the retreat and the obstacles that might be encountered in attempting to implement it.
Subject(s)
Education, Medical/methods , Health Personnel/education , Models, Educational , Patient Care Team , Academic Medical Centers/organization & administration , Academic Medical Centers/trends , Competency-Based Education , Education, Nursing/methods , Education, Pharmacy/methods , HumansABSTRACT
The voltage-gated sodium channel NaV1.5 is responsible for the initial upstroke of the action potential in cardiac tissue. Levels of intracellular calcium modulate inactivation gating of NaV1.5, in part through a C-terminal EF-hand calcium binding domain. The significance of this structure is underscored by the fact that mutations within this domain are associated with specific cardiac arrhythmia syndromes. In an effort to elucidate the molecular basis for calcium regulation of channel function, we have determined the solution structure of the C-terminal EF-hand domain using multidimensional heteronuclear NMR. The structure confirms the existence of the four-helix bundle common to EF-hand domain proteins. However, the location of this domain is shifted with respect to that predicted on the basis of a consensus 12-residue EF-hand calcium binding loop in the sequence. This finding is consistent with the weak calcium affinity reported for the isolated EF-hand domain; high affinity binding is observed only in a construct with an additional 60 residues C-terminal to the EF-hand domain, including the IQ motif that is central to the calcium regulatory apparatus. The binding of an IQ motif peptide to the EF-hand domain was characterized by isothermal titration calorimetry and nuclear magnetic resonance spectroscopy. The peptide binds between helices I and IV in the EF-hand domain, similar to the binding of target peptides to other EF-hand calcium-binding proteins. These results suggest a molecular basis for the coupling of the intrinsic (EF-hand domain) and extrinsic (calmodulin) components of the calcium-sensing apparatus of NaV1.5.
Subject(s)
Calcium-Binding Proteins/chemistry , Calcium/chemistry , Muscle Proteins/chemistry , Myocardium/chemistry , Sodium Channels/chemistry , Amino Acid Motifs/physiology , Arrhythmias, Cardiac/genetics , Arrhythmias, Cardiac/metabolism , Calcium/metabolism , Calcium-Binding Proteins/metabolism , Calmodulin/chemistry , Calmodulin/genetics , Calmodulin/metabolism , Humans , Muscle Proteins/genetics , Muscle Proteins/metabolism , Myocardium/metabolism , NAV1.5 Voltage-Gated Sodium Channel , Nuclear Magnetic Resonance, Biomolecular , Peptides/chemistry , Peptides/genetics , Peptides/metabolism , Protein Binding/physiology , Protein Structure, Tertiary/physiology , Sodium Channels/genetics , Sodium Channels/metabolism , SyndromeABSTRACT
Sodium channels are fundamental signaling molecules in excitable cells, and are molecular targets for local anesthetic agents and intracellular free Ca(2+) ([Ca(2+)](i)). Two regions of Na(V)1.5 have been identified previously as [Ca(2+)](i)-sensitive modulators of channel inactivation. These include a C-terminal IQ motif that binds calmodulin (CaM) in different modes depending on Ca(2+) levels, and an immediately adjacent C-terminal EF-hand domain that directly binds Ca(2+). Here we show that a mutation of the IQ domain (A1924T; Brugada Syndrome) that reduces CaM binding stabilizes Na(V)1.5 inactivation, similarly and more extensively than even reducing [Ca(2+)](i). Because the DIII-DIV linker is an essential structure in Na(V)1.5 inactivation, we evaluated this domain for a potential CaM binding interaction. We identified a novel CaM binding site within the linker, validated its interaction with CaM by NMR spectroscopy, and revealed its micromolar affinity by isothermal titration calorimetry. Mutation of three consecutive hydrophobic residues (Phe(1520)-Ile(1521)-Phe(1522)) to alanines in this CaM-binding domain recapitulated the electrophysiology phenotype observed with mutation of the C-terminal IQ domain: Na(V)1.5 inactivation was stabilized; moreover, mutations of either CaM-binding domain abolish the well described stabilization of inactivation by lidocaine. The direct physical interaction of CaM with the C-terminal IQ domain and the DIII-DIV linker, combined with the similarity in phenotypes when CaM-binding sites in either domain are mutated, suggests these cytoplasmic structures could be functionally coupled through the action of CaM. These findings have bearing upon Na(+) channel function in genetically altered channels and under pathophysiologic conditions where [Ca(2+)](i) impacts cardiac conduction.
Subject(s)
Calcium/metabolism , Calmodulin/metabolism , Muscle Proteins/metabolism , Sodium Channels/metabolism , Amino Acid Motifs/genetics , Amino Acid Substitution , Brugada Syndrome/genetics , Brugada Syndrome/metabolism , Calcium/chemistry , Calmodulin/chemistry , Calmodulin/genetics , Cell Line , Cytoplasm/chemistry , Cytoplasm/genetics , Cytoplasm/metabolism , Humans , Muscle Proteins/chemistry , Muscle Proteins/genetics , Mutation, Missense , NAV1.5 Voltage-Gated Sodium Channel , Nuclear Magnetic Resonance, Biomolecular , Protein Stability , Protein Structure, Quaternary/genetics , Protein Structure, Tertiary/genetics , Sodium Channels/chemistry , Sodium Channels/geneticsABSTRACT
Biomedical science is at an evolutionary turning point. Many of the rate-limiting steps to realizing the next generation of personalized, highly targeted diagnostics and therapeutics rest at the interstices between biomedical science and the classic, university-based disciplines, such as physics, mathematics, computational science, engineering, social sciences, business, and law. Institutes, centers, or other entities created to foster interdisciplinary science are rapidly forming to tackle these formidable challenges, but they are plagued with substantive barriers, born of traditions, processes, and culture, which impede scientific progress and endanger success. Without a more seamless interdisciplinary framework, academic health centers will struggle to move transformative advances in technology into the foundation of biomedical science, and the equally challenging advancement of models that effectively integrate new molecular diagnostics and therapies into the business and social fabric of our population will be similarly hampered. At the same time, excess attention on rankings tied to competition for National Institutes of Health and other federal funds adversely encourages academic medical centers (AMCs) and universities to hoard, rather than share, resources effectively and efficiently. To fully realize their discovery potential, AMCs must consider a substantive realignment relative to one another, as well as with their associated universities, as the academy looks toward innovative approaches to provide a more supportive foundation for the emergent biomedical research enterprise. The authors discuss potential models that could serve to lower barriers to interdisciplinary science, promoting a new synergy between AMCs and their parent universities.
Subject(s)
Academic Medical Centers/organization & administration , Competitive Behavior , Cooperative Behavior , Technology Transfer , Humans , Organizational Culture , Organizational Innovation , ResearchABSTRACT
PURPOSE: In 2000, faced with a national concern over the decreasing number of physician-scientists, Vanderbilt School of Medicine established the institutionally funded Vanderbilt Physician-Scientist Development (VPSD) program to provide centralized oversight and financial support for physician-scientist career development. In 2002, Vanderbilt developed the National Institutes of Health (NIH)-funded Vanderbilt Clinical Research Scholars (VCRS) program using a similar model of centralized oversight. The authors evaluate the impact of the VPSD and VCRS programs on early career outcomes of physician-scientists. METHOD: Physician-scientists who entered the VPSD or VCRS programs from 2000 through 2006 were compared with Vanderbilt physician-scientists who received NIH career development funding during the same period without participating in the VPSD or VCRS programs. RESULTS: Seventy-five percent of VPSD and 60% of VCRS participants achieved individual career award funding at a younger age than the comparison cohort. This shift to career development award funding at a younger age among VPSD and VCRS scholars was accompanied by a 2.6-fold increase in the number of new K awards funded and a rate of growth in K-award dollars at Vanderbilt that outpaced the national rate of growth in K-award funding. CONCLUSIONS: Analysis of the early outcomes of the VPSD and VCRS programs suggests that centralized oversight can catalyze growth in the number of funded physician-scientists at an institution. Investment in this model of career development for physician-scientists may have had an additive effect on the recruitment and retention of talented trainees and junior faculty.